Deprecating regexp field for LOGSTASH-756

- Deprecating fields to columns
- Deprecating regexp fields to source
- Adding target for sub field specifcation
- Added and modified rspec checks
Minor modification to documentation
Deprecating regexp fields

- Replaced regexp fields with source and target variable
- Added tests for new variables
Deprecating regexp fields for json filter

- Replace regexp fields with source and target
- Added test for the new fields
Update patterns/grok-patterns

This is a personal preference, but for web logs, I prefer the parser to capture what it can.  Currently with an invalid request, it fails completely rather than capturing the other log information such as date, bytes transferred and HTTP status.

This patch captures the invalid request into @fields.rawrequest and leaves @fields.verb, @fields.request and @fields.httpversion as nulls if it cannot be properly parsed.

Here is a sample of invalid requests I have from my logs:
115.70.170.86 - - [31/Oct/2012:06:41:24 +1100] "G" 408 0 "-" "-"
165.86.71.20 - - [31/Oct/2012:04:27:01 +1100] "GET http://dis.us.criteo.com/dis/dis.aspx?&t1=sendEvent&c=2&p=3937&p1=v%3D2%26wi%3D7715628%26pt1%3D0%26pt2%3D1%26si%3D1&cb=21664477550&ref=&sc_r=1280x1024&sc_d=32 HTTP/1.0" 400 672 "-" "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)"

Obviously these are not valid requests, and I prefer to handle them this way, but the change is up to you.
LOGSTASH-689: prefix OpenTSDB message with 'put '
piplined and batched eval redis input
more correct code comment
first before doing batched/piplined requests
add a few more tests
some readability changes
move out redis script load from connect method
revert & explicit return
reload batch redis script incase redis was restarted or script cache flushed
Copy amqp output plugin into rabbitmq file
Change AMQP to RabbitMQ names
Remove 'name' field
Remove amqp output plugin
Rename amqp input plugin to rabbitmq
new filter: response code.  translate http response codes to text